1. Field of the Invention
The present invention is related to fine denier fibers. In particular, the invention is related to fine denier fibers obtained by splitting multicomponent fibers having an elastomeric component and to fabrics made from such fibers.
2. Description of the Related Art
Fibers formed of synthetic polymers have long been recognized as useful in the production of textile articles. Such fibers can be used in diverse applications such as apparel, disposable personal care products, medical garments, filtration media, and carpet.
It can be desirable to incorporate fine or ultrafine denier fibers into a textile structure, such as filtration media. Fine denier fibers may be used to produce fabrics having smaller pore sizes, thus allowing smaller particulates to be filtered from a fluid stream. In addition, fine denier fibers can provide a greater surface area per unit weight of fiber, which can be beneficial in filtration applications. Fine denier fibers can also impart u soft feel and touch to fabrics.
Fine denier fibers are also advantageous in producing synthetic yarns and fabrics. Yarns and fabrics made from synthetic fibers aim to be competitive with yarns and fabrics made from natural fibers by simulating spun yarns, and a variety of techniques have been attempted to produce synthetic materials having improved characteristics such as greater bulkiness and softness, superior flexibility and drape, and better barrier and filtration properties.
One method of simulating spun yarns involves cutting continuous synthetic filaments into staple fibers and spinning the staple fibers into yarns by conventional spinning methods used for natural fibers. However, this approach is a time consuming and costly. Alternatively, continuous filaments can be converted into yarns by various texturing methods at lower cost, but these yarns often inadequately simulate spun yarns.
Another technique for converting filament yarns into simulated spun yarns is the air-jet texturing process. In this process, a cold air stream is used to produce loopy bulked yarns of low extensibility. The yarn surface is covered with fixed resilient loops, which serve the same purpose as the protruding hairs in spun yarns by forming an insulating layer of entrapped still air between neighboring layers or garments (see FIG. 5A). Synthetic yarns produced by the air-jet texturing more closely simulate spun yarn structures and resemble spun fiber yarns in their appearance and physical characteristics, although these air-jet textured yarns are not stretchable. Currently, air-jet textured yarns are widely used in outerwear and lighter-wear fabrics, upholstery fabrics and other textile applications. The use of fine denier fibers results in synthetic yarns and fabrics having desirable properties such as good softness and bulkiness as well as good flexibility and fabric drape, with superior filtration and barrier properties and coverage at low weight.
It is, however, difficult to produce fine denier fibers, in particular fibers of 2 denier or less, using conventional melt extrusion processes. Meltblowing technology is one avenue by which to produce fabric from fine denier filaments. However, meltblown webs typically do not have good physical strength, primarily because less orientation is imparted to the polymer during processing and lower molecular weight resins are employed.
Multicomponent or composite fibers having two or more polymeric components may be split into fine fibers comprised of the respective components. The single composite filament thus becomes a bundle of individual component microfilaments. Typically, multicomponent fibers are divided or split by mechanically working the fibers. Methods commonly employed to work fibers include drawing on godet rolls, beating or carding. Fabric formation processes such as needle punching or hydroentangling may supply sufficient energy to a multi component fiber to effect separation.
In addition, fine denier fibers can be prepared using a multicomponent fiber comprised of a desired polymer and a soluble polymer. The soluble polymer is then dissolved out of the composite fiber, leaving microfilaments of the other remaining insoluble polymer. The use of dissolvable matrixes, however, to produce fine denier filaments is problematic. Manufacturing yields are inherently low because a significant portion of the multiconstituent fiber must be destroyed to produce the microfilaments. The wastewater or spent hydrocarbon solvent generated by such processes poses an environmental issue. In addition, the time required to dissolve the matrix component out of the composite fiber further exacerbates manufacturing inefficiencies.
In addition to fine denier fibers, it can also be desirable to incorporate elastomeric fibers into textile structures to impart stretch and recovery properties. Elastomeric fibers or filaments are typically incorporated into fabrics to allow the fabrics to conform to irregular shapes and to allow more freedom of body movement than fabrics with more limited extensibility.
Elastomers used to fabricate elastic fabrics, however, often have an undesirable rubbery feel. Thus, when these materials are used in fabrics, the hand and texture of the fabric can be perceived by the user as sticky or rubbery and therefore undesirable. Non-elastomeric fibers can be commingled with elastomeric fibers and/or coated with an elastomeric solution to improve the feel of articles formed using elastic fibers. However, this requires additional processing steps, which can add manufacturing and materials costs. For example, a stretchable fabric is commonly produced with filament yarns or spun (staple) yarns in combination with an elastic yarn. One commonly used elastic yarn is a wrapped yarn, which has elastic filament yarn, such as Spandex yarn, in the core and wrapped by a synthetic filament yarn (see FIG. 5B). The synthetic filament wrap yarn provides abrasive protection to the elastic core yarn. The process of making such a wrapped yarn is slow and costly. To acquire both soft and stretchable properties, the conventional yarns need to be processed through many steps of blending and twisting, which are impractical and expensive.
Further, it can be difficult to process elastomeric materials to make elastic fibers or filaments. For example, many elastomeric yarns arc formed of solvent spun elastomeric materials (Spandex). Elastomeric yarns can be produced by thermally extruding elastomeric filaments. However, one problem with this approach is breakage or elastic failure during extrusion and drawing. Due to the stretch characteristics of elastomeric polymers, the filaments tend to snap and break while being attenuated. If a filament breaks during production, the ends of the broken filament can either clog the flow of filaments or enmesh the other filaments, resulting in a mat of tangled filaments.
Elastic webs having fine denier elastomeric fibers can be produced using meltblowing technology. However, as noted above, meltblown webs typically do not have good physical strength. In addition, meltblown elastomeric webs generally have less aesthetic appeal.
The present invention provides splittable multicomponent fibers and fiber bundles which include a plurality of fine denier filaments having many varied applications in the textile and industrial sector. The fibers can exhibit many advantageous properties, such as a soft, pleasant hand, high covering power, stretch and recovery and the like. The present invention further provides fabrics formed of the multicomponent fibers and fiber bundles, as well as processes by which to produce fine denier filaments.
In particular, the invention provides thermally divisible or splittable fibers formed of elastomeric components and non-elastomeric components. The elastomeric and non-elastomeric components are selected to have sufficient mutual adhesion to allow the formation of a unitary multicomponent fiber. Indeed, the fibers can be mechanically worked, for example, by drawing, carding, cutting, and the like, without splitting, and without additives to prevent splitting upon mechanical action. Yet the adhesion of the components is sufficiently low so as to allow the components to separate or split when thermally treated.
Specifically, the adhesion of die elastomeric and non-elastomeric components to one another can be defined in terms of the difference of solubility parameters of the elastomeric polymer and the non-elastomeric polymer. In this regard, the elastomeric polymer is selected to have a solubility parameter (xcex4) sufficiently different from the non-elastomeric polymer so that the elastomeric component and the non-elastomeric component split upon thermal activation. Preferably the elastomeric polymer and the non-elastomeric polymer have a difference in solubility parameters (xcex4) of at least about 1.2 (J/cm3)1/2, and more preferably at least about 2.9 (J/cm3)1/2. In one particularly advantageous aspect of the invention, the divisible multicomponent fiber includes at least one polyurethane component and at least one polyolefin, preferably polypropylene, component.
The fibers can have a variety of configurations, including pie/wedge fibers, segmented round fibers, segmented oval fibers, segmented rectangular fibers, segmented ribbon fibers, and segmented multilobal fibers. Further, the thermally splittable multicomponent fibers can be in the form of continuous filaments, staple fibers, or meltblown fibers.
The polymer components are dissociable by thermal means under conditions of low or substantially no tension (i.e., under relaxation) to form a bundle of fine denier elastomeric fibers and fine denier non-elastomeric fibers. The fiber bundle can have desirable stretch and recovery properties as well as desirable aesthetics. Generally the fibers of the invention can be drawn prior to thermal treatment to plastically deform the non-elastomeric components so that they remain drawn even under no stress. Thus the length of the plastically deformed non-elastomeric components is greater than the length of the non-elastomeric components before drawing. In contrast, the elastomeric components are elastically deformed and remain in their stretched or drawn state only because of the friction thereof with the surfaces of the non-elastic components. It has unexpectedly been found that after drawing, thermally treating the multicomponent fibers under relaxation provides sufficient impetus to release the hold of one polymer component on the other. This release allows the elastomeric components to contract, which splits the components of the fibers. In addition to permitting contraction of the elastomeric components, thermal treatment has also been found to shrink the elastomeric components, thereby enhancing the separation of the components of the fibers.
Additionally, the inventors have also found that release of the adhesion forces between the elastomeric and non-elastomeric components by thermal treatment under conditions of low or substantially no tension causes the non-elastomeric filaments to bulk or bunch up around the elastomeric filaments. In effect, as the elastomeric filaments contract and shrink, the force of this elastomeric contraction and shrinkage shortens the length (i.e., the end-to-end straight line distance) occupied by the bundle so that the non-elastomeric filaments (which are longer than the elastomeric filaments) bunch up. This imparts bulk to the resultant fiber bundle to form a xe2x80x9cself bulkedxe2x80x9d or xe2x80x9cself texturizedxe2x80x9d microfilament yarn with elastic stretch. In addition, the bulked non-elastomeric microfilaments bulk around the exterior of the yarn so that the bulked non-elastomeric microfilaments substantially surround or cover the elastomeric filaments. The resultant fiber bundle is elastomeric yet has a pleasant feel due to the bulked non-elastomeric microfilaments covering the surface of the fiber bundle.
This also imparts the ability to provide differential color to the bulked yarn. The elastomeric components and non-elastomeric components can be melt colored with different colors. The yarn will have a first color in its unstretched condition (imparted primarily by the exterior bulked non-elastomeric filaments), and a different color in its stretched condition (imparted by exposure of the differently colored interior elastomeric filaments and a blend of the color of both the elastomeric and non-elastomeric filaments).
The multicomponent fibers can also be formed into elastomeric yarns, for example, by directing the fibers through a conventional texturizing air jet to commingle the fibers. The multicomponent fibers can be thermally treated first to split the multicomponent fibers to form a fiber bundle, and the fiber bundle can thereafter be directed through a texturizing jet to form a bulked yarn. Alternatively, the multicomponent fibers can be simultaneously split and texturized within an air jet to form a bulked yarn.
The multicomponent fibers can also be formed into a variety of other textile structures, including nonwoven, woven and knit fabrics. In this aspect of the invention, the multicomponent fibers can be divided into microfilaments prior to, during, or following fabric formation. The resultant fabrics also exhibit desirable hand and elastic stretch and recovery.
Products comprising the fabric of the present invention provide further advantageous embodiments. Particularly preferred products include synthetic suede fabrics, filtration media, dental floss and synthetic fabrics useful in disposable absorbent articles.
The splittable multicomponent fibers of the invention are generally made by extruding a plurality of multicomponent fibers having at least one elastomeric polymeric component and at least one non-elastomeric polymeric component. The elastomeric and non-elastomeric polymers have solubility parameters sufficiently different so that the elastomeric and non-elastomeric components split upon thermal activation. The multicomponent fibers are advantageously drawn, and then thermally treated under conditions of low or substantially no tension (i.e., under relaxation) to separate the multicomponent fibers to form a fiber bundle of elastomeric microfilaments and non-elastomeric microfilaments. This is contrary to conventional fiber processing steps which are typically conducted while holding the fibers under tension.
Advantageously the fibers are split by contacting the fibers with a heated gaseous medium, such as heated air. Other types of heat can be used, including radiant or steam heat, although the presence of water is not required to achieve splitting. Other types of heating apparatus can also be used, such as hot plates, heated rolls, hot baths (water or oil), microwave energy and the like.
The process also eliminates the need for solvents to dissolve one component or mechanical working to split the fibers. Further, the fibers can be extruded, drawn, and otherwise mechanically worked without substantial premature splitting during these process steps, thus imparting a greater degree of control in initiating splitting. A combination of thermal treatment and subsequent mechanical working can be used to achieve a very high degree of fiber splitting. In addition, the process allows the extrusion of fibers having elastic stretch and recovery properties without the problems typically associated with extruding elastomeric monocomponent fibers.
Still further, the multicomponent fiber can be structured to minimize the occurrence of the elastomer on surfaces of the fibers that come into contact with processing equipment (such as lobe tips). For example a segmented multilobal fiber having a segmented xe2x80x9ccrossxe2x80x9d configuration can be useful in this regard. This can be advantageous in processes in which the fibers contact metal surfaces, such as carding, by reducing fiber-to-metal friction problems associated with some elastomeric fibers, such as polyurethane fibers.
Further understanding of the processes and systems of the invention will be understood with reference to the brief description of the drawings and detailed description which follows herein.